North Korea's summer offensive was brought to an abrupt end on 15 September 1950 with a daring amphibious landing at Inchon. Within a few days, the much-battered North Korean army was disintegrating as it retreated from the Pusan perimeter, pursued by the U.N. Eighth Army. Seoul was liberated by month's end. In October, a further amphibious operation directed against the east coast port city of Wonsan was overtaken by events, as the South Korean army pushed into the objective area well before the planned landing date.

U.N. ground forces, still largely made up of U.S. and South Korean troops, moved north along the Korean east coast, through the center of the peninsula and up into its western parts from Seoul, constrained more by logistics problems than by enemy resistance. Though hampered by severe shortages of mine clearance assets, the Navy opened new ports at Chinnampo on the west coast and Wonsan, Hungnam, Iwon and Songjin in the east. Supplies and fresh forces from across the Pacific, so sparse in July, were by now arriving in abundance. President Truman and other dignitaries came west to confer and to see for themselves.

Offshore, four U.S. fleet aircraft carriers, smaller U.S. and British carriers, several cruisers and numerous destroyers hurled airborne weapons and naval gunfire wherever enemy targets could be found. The available firepower was so abundant that some ships, rushed out during the summer crisis, were released to return home for a well-deserved rest or returned to their normal duties.

A United Nations' resolution offered a mandate to reunify Korea from the south, and General MacArthur willingly complied. However, his troops were thin on the ground in North Korea, with the separate spearheads too separated by distance and the rugged terrain to provide mutual support. From Communist China came threats of intervention, unfortunately discounted by MacArthur's intelligence, as the Chinese intent was real and was backed by battle-hardened ground forces and a Soviet promise of covering air power.

By early November, U.S. and South Korean troops had fought Chinese units, capturing prisoners and discovering that the new enemy was a tough one. Aerial reconnaissance reported much military traffic southbound from Manchuria. MacArthur was concerned enough to begin bombing attacks against bridges over the Yalu, but retained his optimism that a final offensive in late November would quickly bring the War to a successful conclusion.